SyntaxHighlighter - Scala Example

      package examples

      /** Illustrate the use of pattern matching in Scala.
       *  Like patterns.scala, but uses extractors for representation independence
       */
      object extractorPatterns {

        /** We need an abstract base class for trees. Subclasses with
         *  the 'case' modifier can be used in pattern matching expressions
         *  to deconstruct trees.
         *
         *  Here, we replaced case classes of patterns.scala with objects
         *  that hide the actual implementation of Branch and Leaf. Note
         *  that the remaining code does not change. In this way, we
         *  can change the implementation later without affecting clients,
         *  which is called representation independence.
         */
        abstract class Tree

        object Branch {
          /* method to contruct branches @see extractorPatterns.tree1 */
          def apply(left: Tree, right: Tree): Tree = new BranchImpl(left, right)
          /* extractor method referenced in match expressions @see extractorPatterns.sumLeaves */
          def unapply(x:Tree): Option[(Tree,Tree)] = x match {
            case y:BranchImpl => Some(y.left, y.right)
            case _            => None
          }
          private class BranchImpl(val left:Tree, val right:Tree) extends Tree
        }
        object Leaf {
          /* method to contruct leaves @see tree1 */
          def apply(x:Int): Tree = new LeafImpl(x);
          /* extractor method referenced in match expressions @see extractorPatterns.sumLeaves */
          def unapply(x:Tree): Option[Int] = x match {
            case y:LeafImpl => Some(y.x)
            case _          => None
          }
          private class LeafImpl(val x: Int) extends Tree
        }


        /** Case classes have an implicit constructor methods which allows
         *  to create objects withouth the 'new' keyword. It saves some typing
         *  and makes code clearer.
         *
         *  Here, the task of the case class constructor is performed by the
         *  method Branch.apply - the singleton Branch is treated as if it
         *  were a function value. This trick works with any value that has
         *  an apply method.
         */
        val tree1 = Branch(Branch(Leaf(1), Leaf(2)), Branch(Leaf(3), Leaf(4)))

        /** Return the sum of numbers found in leaves.
         *  'match' is a generalization of 'switch' in C-like languages
         *
         *  Patterns consist of case class constructors (which can
         *  be nested), and lower case variables which are
         *  bound to the values with which the class has been constructed.
         *
         *  For extractors, it is not the name of a case class, but the name of
         *  the singleton object Branch which is used to refer to its extractor method
         *  Branch.unapply - the pattern is the 'reverse' of a method
         *  call, with the result being matched in the subpatterns. This works
         *  for any value that has an appropriate extractor method.
         */
        def sumLeaves(t: Tree): Int = t match {
          case Branch(l, r) => sumLeaves(l) + sumLeaves(r)
          case Leaf(x) => x
        }

        /** This illustrates the use of Option types. Since the
         *  method is not known in advance to find 'x', the
         *  return type is an Option. Options have two possible
         *  values, either 'Some' or 'None'. It is a type-safe
         *  way around 'null' values.
         */
        def find[A, B](it: Iterator[Pair[A, B]], x: A): Option[B] = {
          var result: Option[B] = None
          while (it.hasNext && result == None) {
            val Pair(x1, y) = it.next;
            if (x == x1) result = Some(y)
          }
          result
        }

        def printFinds[A](xs: List[Pair[A, String]], x: A) =
          find(xs.elements, x) match {
            case Some(y) => println(y)
            case None => println("no match")
          }

        def main(args: Array[String]) {
          println("sum of leafs=" + sumLeaves(tree1));
          printFinds(List(Pair(3, "three"), Pair(4, "four")), 4)
        }
      }

Brush name	Brush aliases	File name
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Bash/shell	bash, shell	shBrushBash.js
ColdFusion	cf, coldfusion	shBrushColdFusion.js
C#	c-sharp, csharp	shBrushCSharp.js
C++	cpp, c	shBrushCpp.js
CSS	css	shBrushCss.js
Delphi	delphi, pas, pascal	shBrushDelphi.js
Diff	diff, patch	shBrushDiff.js
Erlang	erl, erlang	shBrushErlang.js
Groovy	groovy	shBrushGroovy.js
JavaScript	js, jscript, javascript	shBrushJScript.js
Java	java	shBrushJava.js
JavaFX	jfx, javafx	shBrushJavaFX.js
Perl	perl, pl	shBrushPerl.js
PHP	php	shBrushPhp.js
Plain Text	plain, text	shBrushPlain.js
PowerShell	ps, powershell	shBrushPowerShell.js
Python	py, python	shBrushPython.js
Ruby	rails, ror, ruby	shBrushRuby.js
Scala	scala	shBrushScala.js
SQL	sql	shBrushSql.js
Visual Basic	vb, vbnet	shBrushVb.js
XML	xml, xhtml, xslt, html, xhtml	shBrushXml.js

SyntaxHighlighter 3.0.83

Scala Example